Standard Radiation Dose?

tercure

Below is verbatim from the NCCN Guidelines for treatment of anal cancer.

PRINCIPALS OF RADIATION THERAPY

*Multifield techniques with supervoltage radiation (photon energy of >6 mV) should be used to deliver a minimum dose of 45 Gy in 1.8 Gy-fractions (25 fractions over 5 weeks) to the primary cancer

*PET-CT should be considered for treatment planning

*The inguinal nodes and the pelvis, anus, and perineum should be included in the initial radiation fields.  The superior field border should be at L5-S1, and the inferior border should include the anus with a minimum 2.5 cm-margin around the anus and tumor.  The lateral border should include the lateral inguinal nodes (as determined from imaging or bony landmarks).  There should be attempts to reduce the dose to the femoral heads.

*After 17 fractions (30.6 Gy), an additional 14.4 Gy should be given in 8 fractions with the superior field reduced to the bottom of the sacroiliac joints.  Additional field reduction off inguinal nodes should occur after 36 Gy for node-negative lesions.  This protocol brings the total dose to 45 Gy in 25 fractions over 5 weeks.

*For patients treated using an AP-PA technique, rather than the recommended multifield technique, the dose to the lateral inguinal region should be brought to the minimum dose of 36 Gy using an anterior electron boost matched to the PA exit field.

*For T2 lesions with residual disease after 45 Gy, T3/4 lesions, or N1 lesions, an additional boost of 9-14 Gy in 1.8-2 Gy fractions to the original primary tumor volume and involved nodes plus a 2-2.5 cm margin is usually delivered.  This boost brings the total dose to 54-59 Gy in 30-32 fractions over 6-7.5 weeks.  A direct perineal boost using photons or electrons with the patient in lithotomy position or a multifield photon approach (AP-PA plus paired lateral, PA + laterals, or other) can be used.

*The consensus of the panel is that IMRT may be used in place of 3-D conformal RT in the treatment of anal carcinoma.  IMRT requires expertise and careful target design to avoid reduction in local control by so-called "marginal-miss."  The clinical target volumes for anal cancer used in the RTOG-0529 trial have been described in detail. 

*Side effect management:  Female patients should be considered for vaginal dilators and instructed on the symptoms of vaginal stenosis.  Male patients should be counseled on infertility risks and given information regarding sperm banking.  Female patients should be counseled on infertility risks and given information regarding oocyte, egg or ovarian tissue banking prior to treatment.

 

I hope this information will answer your questions.  It makes sense, but may require reading more than once to understand, given that we are not dosimetrists or radiation oncologists.  The bottom line, as I understand it, is radiation dose is calculated according to tumor size and whether or not there is node involvement.  I was staged right on the line between stage 1 and stage 2 and had no node involvement.  I received a total of 54 Gy and my treatment field was reduced twice, with the last few treatments focused directly and only on the tumor. 

mp327 said:

tercure

Below is verbatim from the NCCN Guidelines for treatment of anal cancer.

PRINCIPALS OF RADIATION THERAPY

*Multifield techniques with supervoltage radiation (photon energy of >6 mV) should be used to deliver a minimum dose of 45 Gy in 1.8 Gy-fractions (25 fractions over 5 weeks) to the primary cancer

*PET-CT should be considered for treatment planning

*The inguinal nodes and the pelvis, anus, and perineum should be included in the initial radiation fields.  The superior field border should be at L5-S1, and the inferior border should include the anus with a minimum 2.5 cm-margin around the anus and tumor.  The lateral border should include the lateral inguinal nodes (as determined from imaging or bony landmarks).  There should be attempts to reduce the dose to the femoral heads.

*After 17 fractions (30.6 Gy), an additional 14.4 Gy should be given in 8 fractions with the superior field reduced to the bottom of the sacroiliac joints.  Additional field reduction off inguinal nodes should occur after 36 Gy for node-negative lesions.  This protocol brings the total dose to 45 Gy in 25 fractions over 5 weeks.

*For patients treated using an AP-PA technique, rather than the recommended multifield technique, the dose to the lateral inguinal region should be brought to the minimum dose of 36 Gy using an anterior electron boost matched to the PA exit field.

*For T2 lesions with residual disease after 45 Gy, T3/4 lesions, or N1 lesions, an additional boost of 9-14 Gy in 1.8-2 Gy fractions to the original primary tumor volume and involved nodes plus a 2-2.5 cm margin is usually delivered.  This boost brings the total dose to 54-59 Gy in 30-32 fractions over 6-7.5 weeks.  A direct perineal boost using photons or electrons with the patient in lithotomy position or a multifield photon approach (AP-PA plus paired lateral, PA + laterals, or other) can be used.

*The consensus of the panel is that IMRT may be used in place of 3-D conformal RT in the treatment of anal carcinoma.  IMRT requires expertise and careful target design to avoid reduction in local control by so-called "marginal-miss."  The clinical target volumes for anal cancer used in the RTOG-0529 trial have been described in detail. 

*Side effect management:  Female patients should be considered for vaginal dilators and instructed on the symptoms of vaginal stenosis.  Male patients should be counseled on infertility risks and given information regarding sperm banking.  Female patients should be counseled on infertility risks and given information regarding oocyte, egg or ovarian tissue banking prior to treatment.

 

I hope this information will answer your questions.  It makes sense, but may require reading more than once to understand, given that we are not dosimetrists or radiation oncologists.  The bottom line, as I understand it, is radiation dose is calculated according to tumor size and whether or not there is node involvement.  I was staged right on the line between stage 1 and stage 2 and had no node involvement.  I received a total of 54 Gy and my treatment field was reduced twice, with the last few treatments focused directly and only on the tumor. 

NCCN Info

Thanks for posting that explanation - and Thom that was a good question.  I don't know why I never thought to learn more about the radiation treatment.  For some reason I researched more about the chemo medicines, even though they told me that the radiation would be the primary weapon against this type of cancer, the chemo having more of a supporting role.